An internal combustion engine may include a fuel injection system configured to inject fuel directly into one or more engine cylinders via a fuel injector coupled to each cylinder. Injecting fuel directly into each cylinder (as opposed to injecting fuel into an intake air path upstream of each cylinder) may increase an efficiency of combustion of an air/fuel mixture within each cylinder due to an increased control over the amount of fuel injected. Fuel pressure is often increased by a high-pressure pump coupled to one or more fuel rails prior to injection of the fuel into one or more cylinders. Each fuel rail is coupled to one or more of the fuel injectors in order to flow pressurized fuel from the high-pressure pump towards the fuel injectors. As engine load increases, a temperature of each fuel rail may increase due to proximity of each fuel rail to the engine and its components. If fuel rail temperature is not measured and/or controlled, a temperature of fuel within each fuel rail may increase until the fuel reaches a temperature of vaporization. Injection of vaporized fuel into engine cylinders may result in degradation of the cylinders and/or fuel system components. As a result, engine performance may decrease. Additionally, if the temperature of fuel within each fuel rail is different at one or more fuel injectors, a density of the fuel at the one or more fuel injectors may be different and too much or too little fuel may be injected.
Attempts to address the issues described above by determining fuel rail temperature include inferring the fuel rail temperature based on an output of one or more devices coupled to an inlet of a fuel rail. One example approach is shown by Jung et al. in DE 102007053408. Therein, temperature of fuel within a fuel rail is inferred by measuring an electrical resistance of a coil coupled to a fuel pressure valve and/or a fuel flow valve.
However, the inventors herein have recognized potential issues with such systems. As one example, inferring temperature of fuel within a fuel rail based on conditions at a fuel pressure valve or fuel flow valve does not provide information about a temperature of the fuel at specific locations along the fuel rail (for example, at one or more fuel injectors). Additionally, due to the proximity of each fuel rail to the fuel injectors (and therefore, the engine cylinders), a space may not be available to accommodate temperature sensing devices arranged near the fuel injectors (for example, sensing devices such as the coil described above).
In one example, the issues described above may be addressed by a fuel injection system, comprising: at least one fuel rail; a plurality of fuel injectors coupled to the at least one fuel rail; and a plurality of metal film thermocouples directly bonded to the at least one fuel rail. In this way, temperatures of the fuel rail at a plurality of locations are measured directly at one or more surfaces of the fuel rail, and fuel rail conditions and/or fuel injector nozzle opening times may be adjusted in response to the measured temperatures.
As one example, a pressure of fuel within the fuel rail may be increased in response to one or more of the measured temperatures exceeding a threshold temperature. By adjusting the pressure of the fuel within the fuel rail in response to the measured temperatures, a likelihood of fuel vaporization within the fuel rail may be decreased. Additionally, by adjusting fuel injector nozzle opening times in response to the measured temperatures, a controlled amount of fuel may be delivered to each cylinder in situations where a density of the fuel is different at one or more locations along the fuel rail (due to a difference in fuel temperature at the one or more locations). By controlling the fuel pressure and fuel injector nozzle opening times in this way, fuel may be injected into each cylinder with increased precision, and engine performance may be increased (e.g., via reduced emissions and increased engine torque output).
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.